1. Field of the Invention
The present invention relates to dye diffusion thermal transfer printing, which should be taken to cover sublimation transfer printing, and relates particularly to the efficient use of dye in such printing, the term "dye" being taken to cover dyes, inks and other soluble colorants.
2. Description of the Prior Art
In diffusion thermal transfer printing, heat is applied to selected pixel areas of a dye donor sheet or ribbon by a suitable heat source, such as a series of resistive heating wires or a scanning laser beam. This heating causes diffusion of dye in the selected areas, and transfer of the dye to form printed pixels on an adjacent receiver sheet or ribbon.
The transfer may also be by sublimation, wherein the heating of the donor sheet causes the dye to enter the vapour phase. The dye then crosses an air gap and condenses onto the surface of the receiver sheet from where it may then diffuse inwards.
After printing, the dye sheet or ribbon is left with a number of dye depleted pixel areas where the dye has transferred to the receiver. The dye sheet or ribbon cannot therefore be reused, and must be discarded after a single print from the sheet or after the end of the ribbon is reached. This is wasteful, as much dye still remains on the dye sheet or ribbon in the regions which were not printed from.